The specific aim of this new research proposal is to elucidate the mechanisms and consequences of the interaction between bacteriophage T7 gene 2 protein (gp2) and the host Escherichia coli RNA polymerase, as a model virus-host interaction system. The unique early to late transcriptional switch in T7 development involves an inactivation of the host RNA polymerase. We have identified and purified gp2 as the specific inhibitor of the enzyme. On the other hand, if E. coli RNA polymerase is not inhibited, either in T7 2 minus mutant phage infection or in a mutant host Y49 with gp2 minus resistant RNA polymerase infected with T7 plus phage, uninhibited enzyme perturbs T7 DNA packaging from concatemer DNA. Therefore, 1) We aim to determine the gp2 binding site on E. coli RNA polymerase to elucidate the mechanism of enzyme inactivation and the effect of mutational changes on the function and structure of enzyme subunits and gp2. 2) We aim to determine at what step and how E. coli RNA polymerase blocks T7 DNA packaging. Since the inactivation of the enzyme by gp2 is due to its direct association with the enzyme thus preventing the enzyme to bind T7 DNA, we plan to demonstrate binding of the enzyme to T7 concatemer DNA, inhibition of the binding by gp2, and the effect of the binding on subsequent DNA packaging.